Hardware Reference
In-Depth Information
cult for the BIOS. Therefore, another standard was developed by Intel, Microsoft, and
Toshiba. Called Advanced Configuration and Power Interface (ACPI) , this standard was
designed to implement power-management functions in the OS. Microsoft Windows 98
and later automatically use ACPI if ACPI functions are found in the system BIOS. The
need to update system BIOSs for ACPI support is one reason many computer vendors
have recommended performing a BIOS update before installing Windows 98 or later on
older systems.
ACPI was initially released in 1996 and first appeared in the Phoenix BIOS around that
time. ACPI became a requirement for the Intel/Microsoft “PC'97” logo certification in
1996, which caused developers to work on integrating ACPI into system designs around
that time. Intel included ACPI support in chipsets starting with the PIIX4E South Bridge
in April 1998, and ACPI support was included in Windows starting with the release of
Windows 98 (June 25, 1998) as part of what Microsoft called its “OnNow” initiative. By
the time Windows 2000 came out (February 17, 2000), ACPI had universally replaced
APMonnewsystems.ACPI4.0awasreleasedinApril2010,andtheACPI5.0Specifica-
tion is currently under development. The official ACPI specifications can be downloaded
from www.acpi.info .
Placing power management under the control of the OS enables a greater interaction with
applications.Forexample,aprogramcanindicatetotheOSwhichofitsactivitiesarecru-
cial, forcing an immediate activation of the hard drive, and which can be delayed until the
nexttimethedriveisactivatedforsomeotherreason.Forexample,awordprocessormay
be set to automatically save files in the background, which an OS using ACPI can then
delayuntilthedriveisactivatedforsomeotherreason,resultinginfewerrandomspin-ups
of the drive.
ACPI goes far beyond the previous standard, APM, which consisted mainly of processor,
harddisk,anddisplaycontrol.ACPIcontrolsnotonlypowerbutalsoallthePlugandPlay
(PnP) hardware configuration throughout the system. With ACPI, system configuration
(PnP) and power-management configuration are no longer controlled via the BIOS Setup;
they are instead controlled entirely within the OS.
ACPIenablesthesystemtoautomaticallyturninternalperipheralsonandoff(suchasCD-
ROM drives, network cards, hard disk drives, and modems) as well as external devices
suchasprinters,monitors,oranydevicesconnectedtoserial,parallel,USB,video,oroth-
er ports in the system. ACPI technology also enables peripherals to turn on or wake up
the system. For example, a telephone answering machine application can request that it
be able to respond to answer the telephone within 1 second. Not only is this possible, but
if the user subsequently presses the power or sleep button, the system only goes into the
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